1. Field of the Invention
The present disclosure relates to a reflective type or transmissive and reflective type liquid crystal display (LCD) device and a method of manufacturing the same, more particularly to a reflective type or transmissive and reflective type LCD device and a method of manufacturing the same in which reflectivity of light viewed from a plurality of directions is enhanced regardless of an incident angle of light incident into the LCD device.
2. Description of the Related Art
An LCD device has advantages over other display devices, for example CRT type display device. In detail, the LCD device may be manufactured in a thinner and lighter structure having a lower power consumption, may require a lower driving voltage compared with the other display devices, and may provide image display quality similar to that of the CRT type display device. The LCD device is widely used in various electronic apparatus.
The LCD device is classified into a transmissive type LCD device and a reflective type LCD device. The transmissive type LCD device uses internal light source such as backlight so as to display image, and the reflective type LCD device uses external light source such as a natural sunlight.
The reflective type LCD device needs lower power consumption and provides better display quality when image is displayed outdoors compared with the transmissive type LCD device. However, since the reflective type LCD device does not require external light source such as the backlight, the reflective type LCD device may have a thinner and lighter structure than the transmissive type LCD device.
In the reflective type LCD device, external light is reflected by reflective electrode comprised of a high reflective material such as aluminum (Al) or silver (Ag) for the purpose of image displaying.
Recently, in the reflective type LCD device and a reflective and transmissive type LCD device, two methods are simultaneously used so as to enhance the brightness of the LCD device. Reflectivity efficiency of the reflective electrode is enhanced according to a first method, and high opening ratio is provided according to a second method.
In the reflective type LCD device and a reflective and transmissive type LCD device, when the surface of reflection electrode does not have an embossing pattern but have a flat shape, the brightness of the LCD device varies according to the location on the reflective electrode onto which the external light is incident, so that the brightness of the LCD device may be high at a certain viewing angle. Accordingly, the reflective efficiency is reduced.
Therefore, a method in which the reflective electrode has embossing portions (bumps and dents) so as to enhance the reflective efficiency is disclosed in U.S. Pat. No. 5,610,741 (entitled “Reflection type Liquid Crystal Display Device with bumps on the reflector” and allowed to the inventor Naofumi Kimura).
FIG. 1A is a plan view showing a photomask pattern for forming a reflective electrode having embossing portions that have symmetrically inclined faces according to a conventional LCD device, and FIG. 1B is a sectional view cut along a line A1-A1′ in FIG. 1A.
Referring to FIGS. 1A and 1B, the reflective electrode according to a conventional Thin Film Transistor (TFT) LCD device has convex portions formed in a convex region 10 and concave portions formed in a concave region 12.
The concave portion has a relatively lower height than the convex portion, and the concave region 12 may have a predetermined width. The convex portion has a relatively higher height than the concave portion, and to thereby function as a micro lens.
According to the conventional TFT LCD device of FIG. 1A, embossing portions are formed on an organic insulating layer of a TFT substrate by means of the photomask pattern of FIG. 1A so as to enhance the reflective efficiency, a reflective layer is coated on the organic insulating layer, and so that the reflective electrode is formed on the organic insulating layer to have embossing portions.
According to a structure of the reflective electrode in the conventional LCD device, since the micro lens has a polygonal isotropic structure, the reflective electrode of the conventional LCD device may have an isotropic reflectivity for a whole angle (360°) of directions. As a result, the reflectivity and display quality of an LCD panel are enhanced, so that the LCD panel provides a high brightness for whole angle of directions.
Light is anisotropically incident into the LCD panel when the electronic display devices using the LCD panel, for example a small (or middle) size of cellular phone or a personal digital assistant (PDA), are in use at an user's hand. The intensity of the light incident from user's body (or from 6 o'clock position with respect to the user) into the LCD panel is very weak since most of the light incident from user's body is screened by the user's body. However, the intensity of the light incident from 12 o'clock position with respect to the user is strong. When a reflective electrode having an isotropic reflectivity is employed in above electronic display devices, the reflective efficiency may not be optimized.
A reflector including surface deformity portions (convex portions and concave portions) each having asymmetric cross sections so as to enhance the reflective efficiency in a particular direction is disclosed in U.S. Pat. No. 6,097,458.
FIG. 2A is a plan view showing a photomask pattern for forming a reflective electrode having embossing portions that have faces inclined asymmetrically in a direction according to a conventional LCD device, and FIG. 2B is a cross-sectional view cut along a line A2-A2′ in FIG. 2A. Especially, FIG. 2A shows a portion of the photomask pattern that is formed so as to enhance the reflectivity in a 12 o'clock direction.
Referring to FIG. 2A and FIG. 2B, the reflective electrode includes convex portions formed in a convex region 20 and concave portions formed in a concave region 22. In addition, slit patterns 24 are formed at a certain regions of the convex portions so as to enhance the reflectivity in a 12 o'clock direction. An exposure amount supplied to the regions of the convex portions is regulated through a slit exposure by using the diffraction of the light that passes through the slit patterns 24, so that a profile of the convex portion is asymmetric.
When the reflective electrode has slit patterns treated (arranged) in a first direction (for example 12 o'clock direction) by the slit exposure, the reflectivity increases in the first direction, but the reflectivity may not be enhanced in other directions (for example 9, 6, 3 o'clock directions). Especially, according to the conventional LCD device, the reflectivity and viewing angle cannot be enhanced in various directions.